D. Schofield 23 
DIELECTRIC CONSTANT “/e, (10%) 
Fig. 1.16. Variation of dielectric 
constant with hydrostatic pressure. 
ie) 2 4 6 8 10 12 
PRESSURE (10°PS1) 
Barium titanate has atetragonal structure, the elongatedaxis being the direc- 
tion of polarization. The application of planar compressional stress to ceramic 
barium titanate tends to align the elongated axis, or c axis, normal to the plane 
of the stress. Since the intrinsic permittivity is considerably smaller along the 
c axis, than in the adirection,this domain alignment should result in a reduction 
of the contribution to the total dielectric constant from the intrinsic permittivity 
of the domains. There are other contributions tothe total dielectric constant (see 
[18]), but this is sufficient to illustrate one effect of stress and to suggest that 
other parameters of the materials may also be affected. Figure 1.16 shows the 
LL LL LL} 
DIELECTRIC CONSTANT K 
fo) ) 3 fo) ° 
fo) = nN ol > 
fo} °o fo) fo} fo} 
o 
o 
fe) 
0.1 ! 10 100 
TIME (MINUTES) 
Fig. 1.17. Aging of dielectric constant following application of 9000 psi 
to a barium titanate sphere. 
